Nowadays, magnetic devices such as transformers and inductors are widely used in many electrical apparatuses to generate induced magnetic fluxes. Nowadays, the electrical apparatus is developed toward to have small size and reduced volume. Consequently, the magnetic device and the conductive winding assembly of the magnetic device need to have slim appearance.
Take a conventional transformer for example. FIG. 1 is a schematic exploded view illustrating a conventional transformer. As shown in FIG. 1, the conventional transformer 1 includes a magnetic core assembly 11, a bobbin 12, a primary winding coil 13, and a secondary winding coil 14. The primary winding coil 13 and the secondary winding coil 14 are overlapped with each other and wound around a winding section 121 of the bobbin 12. An isolating tape 2 is provided for isolation and insulation. The bobbin 12 further includes a channel 122. Several pins 123 are disposed on the bottom surfaces of the both sides of the bobbin 12. The pins 123 are connected with the primary winding coil 13 and the secondary winding coil 14. Via pins 123, the primary winding coil 13 and the secondary winding coil 14 are electrically connected with a circuit board (not shown). As shown in FIG. 1, the magnetic core assembly 11 is an EE-type magnetic core assembly. The magnetic core assembly 11 includes a first magnetic core 111 and a second magnetic core 112. The first magnetic core 111 has a first middle portion 111a, and the second magnetic core 112 has a second middle portion 112a. 
For assembling the transformer 1, the first middle portion 111a of the first magnetic core 111 and the second middle portion 112a of the second magnetic core 112 are firstly aligned with and embedded into the channel 122 of the bobbin 12, and then the first magnetic core 111 and the second magnetic core 112 are combined together. Consequently, the primary winding coil 13 and the secondary winding coil 14 interact with the first magnetic core 111 and a second magnetic core 112 of the magnetic core assembly 11 to achieve the purpose of voltage regulation.
Generally, the bobbin 12 of the transformer 1 is made of a plastic material. Since the bobbin 12 includes the winding section 121, the channel 122 and other structures, the volume and thickness of the bobbin 12 are very large. Moreover, after the primary winding coil 13 and the secondary winding coil 14 are wound around the winding section 121 of the bobbin 12 and the magnetic core assembly 11 is assembled with the bobbin 12, the volume of the bobbin 12 is increased. In other words, it is difficult to slim the conventional transformer 1.
Moreover, after the primary winding coil 13 and the secondary winding coil 14 are overlapped with each other and wound around the winding section 121 of the bobbin 12, the primary winding coil 13 and the secondary winding coil 14 are connected to the pins 121. If the safety distance is insufficient, the exposed parts of the primary winding coil 13 and the secondary winding coil 14 are readily suffered from high-voltage spark. Consequently, the transformer 1 is easily damaged.
Therefore, there is a need of providing an improved magnetic device so as to obviate the drawbacks encountered in the prior art.